Field of the Invention
The present invention concerns a magnetic resonance apparatus with: a magnet unit that has at least one superconducting coil that generates a basic magnetic field, a magnet housing unit surrounding the at least one superconducting coil, a cooling system that has at least one cooling loop, and a heat absorption unit to cool the at least one superconducting basic magnetic coil; and an additional unit.
Description of the Prior Art
Magnetic resonance devices normally have a cooling system with two cooling loops to cool the superconducting that generate the basic magnetic field coils. A first cooling loop thermally couples to a cryostat unit with a helium compressor and a cryo-head that is designed to cool helium at temperatures of approximately −270° C. Waste heat of the cryostat unit is transferred to the first cooling loop. A second cooling loop of the cooling system thermally couples to the first cooling loop so that heat energy of the first cooling loop is transferred to the second cooling loop. It is therefore ensured that the first cooling loop always exhibits an advantageous cooling temperature for cooling the cryostat unit.
If a failure of the second cooling loop now occurs, cooling of the superconducting basic magnetic coil is no longer ensured since this ultimately also leads to an overheating and/or a deactivation of the first cooling loop. The deactivation of the first cooling loop is required in the event of a failure of the second cooling loop, since a transfer of waste heat away from the first cooling loop (and therefore from the cryostat unit) is no longer provided. If the cryostat unit (in particular the helium compressor and the cryo-head) can no longer be operated, this leads to a vaporization of the helium that is present in a helium vessel of the cryostat unit, and therefore increases a helium pressure in the helium vessel. If the helium pressure exceeds a limit value, the helium begins to escape from the helium pressure, such that high costs can occur due to the replacement of helium for the operation of the magnetic resonance apparatus. For example, given a failure of the cooling system, a vaporization rate can encompass approximately 2 l to 3 l of liquid helium per hour.
This problem is especially disadvantageous in magnetic resonance apparatuses with reduced helium fill volumes. In such apparatuses, the fill level of liquid helium within the helium vessel that is required for a safe operation of the magnetic resonance device can already fall below a minimum after only a short duration of a failure of the cooling system.